This invention generally relates to water jet apparatus for propelling boats and other watercraft. In particular, the invention relates to mechanisms for shifting a water jet apparatus to selectively propel a craft in the forward or reverse direction.
It is known to propel a boat or other watercraft using a water jet apparatus mounted to the hull, with the powerhead being placed inside (inboard) the hull. An impeller is mounted on a shaft driven by a drive shaft of the motor, and is housed in a duct having an inlet and an outlet. The impeller is designed such that during motor operation, the rotating impeller impels water rearward through the duct. The water discharged from the duct outlet produces a thrust which propels the boat forward.
In addition, it is known to provide a mechanism for diverting the discharged water flow to one side or the other of a midplane, thereby enabling the boat operator to steer the boat to the left or right during forward propulsion. One such mechanism is a steering nozzle pivotably mounted to the duct and in flow communication with the duct outlet. Preferably the pivot axis of the steering nozzle lies in the midplane. As the steering nozzle is pivoted to the left of a central position, the water flow out of the duct is diverted leftward, producing a thrust which pushes the water jet apparatus and the boat stern to the right, thereby causing the bow of the boat to turn to the left. Similarly, the boat bow turns to the right when the steering nozzle is pivoted to the right of the central position.
It is also known to provide a mechanism for reversing the direction of the water flow exiting the steering nozzle. The reverse gate can be pivotably mounted to the steering nozzle, its pivot axis being generally perpendicular to the pivot axis of the steering nozzle. In the up position, the reverse gate is clear of the water flow exiting the steering nozzle. In the down position, the reverse gate is disposed in the path of the exiting water flow. In its simplest embodiment, the reverse gate has a U-shaped channel which reverses the water flow exiting the steering nozzle. In other words, when the steering nozzle is turned to the left, the resulting water flow having rearward and leftward flow components is redirected by the reverse gate to have forward and rightward components. This produces a thrust which pulls the boat rearward and propels the water jet apparatus and boat stern to the left, causing the boat to turn left during rearward movement. Similarly, the boat turns to the right during rearward movement when the steering nozzle is turned to the right. The provision of a steerable reverse gate allows the boat operator to steer in forward and reverse in the same manner that an automobile can be steered.
In accordance with other known designs, the reverse gate is not steerable, i.e., the reverse gate is pivotably mounted to the water jet housing. In the up position, the reverse gate is clear of the water flow exiting the steering nozzle; in the down position, the reverse gate obstructs the water flow exiting the steering nozzle and reverses the rearward flow component. Some non-steerable designs also reverse the lateral flow component; others do not. The non-steerable reverse gate designs which reverse the lateral flow component cause the rearward-moving boat to turn left when the steering nozzle is turned to the left and to turn right when the steering nozzle is turned to the right. However, these prior designs provide less than optimal reverse thrust and steering thrust. There is a need for a non-steerable reverse gate which reverses the lateral flow component, provides increased reverse and steering thrusts, and operates with low cable loads.
The present invention is directed to a non-steerable reverse gate having a structure which reverses the lateral flow component when the steering nozzle is turned. The reverse gates in accordance with the preferred embodiments produce high reverse and steering thrusts, while requiring low operating loads. The steering response in reverse is the same as an outboard or inboard/outboard. In effect, the transom thrusts to the side that the steering wheel is turned to. The invention is also directed to a water jet propulsion system having a non-steerable reverse gate of the foregoing type.
In accordance with one preferred embodiment of the invention, the reverse gate comprises a pair of flow-reversing passages for providing reverse thrust, a lateral steering passage for producing a lateral thrust when the steering nozzle is turned, and a fixed central deflector body. In accordance with another preferred embodiment, the central deflector body is pivotable about a vertical axis.
In accordance with both preferred embodiments disclosed herein, the flow-reversing passages are located on opposite (i.e., port and starboard) sides of the reverse gate. Each flow-reversing passage has an inlet and an outlet. The lateral steering passage is located aft of the deflector body and reversing passages and has discharge openings on opposite ends thereof, i.e., on the port and starboard sides of the reverse gate. The lateral steering passage communicates with the main chamber of the reverse gate via an aperture which is centered between port and starboard curved outer walls of the reverse gate. These port and starboard curved outer walls extend forward and laterally outward to form the outer side walls of the flow-reversing passages. The central aperture allows some of the water discharged from the steering nozzle to enter the lateral steering passage. The deflector is situated in front of the aperture to deflect some of the pump discharge to the sides and into the flow-reversing passages.
The deflector body in accordance with the first preferred embodiment of the invention comprises three vertical walls connected at a central vertical line located midway between the reversing passage inlets. The three vertical walls are preferably attached or joined to the top and bottom walls of the reverse gate housing. One vertical wall of the deflector body lies in the reverse gate midplane and extends forward from the central juncture of the walls. The other vertical walls of the deflector body are laterally curved in the shape of respective arcs. One arc curves from the central juncture toward the inlet of the reversing passage on the port side of the reverse gate; the other arc curves from the central juncture toward the inlet of the reversing passage on the starboard side of the reverse gate. These curved vertical walls will be referred to herein as flow-deflecting walls. The concave side of each flow-deflecting wall faces toward a wide opening in the front of the reverse gate, through which the water discharged from the steering nozzle outlet flows into the reverse gate. The flow-deflecting walls respectively guide or deflect incoming water toward the respective inlets of the opposing reversing passages. The incoming stream of water is split by the central vertical wall into two streams which respectively flow along the front surfaces of the curved vertical walls. In accordance with the preferred embodiment, the port surface of the central vertical wall and the front surface of the curved vertical wall on the port side form a continuous surface having a J-shaped contour which redirects one stream of incoming water toward the port reversing passage; similarly, the starboard surface of the central vertical wall and the front surface of the curved vertical wall on the starboard side form a continuous surface having a J-shaped contour which redirects the other stream of incoming water toward the starboard reversing passage.
In accordance with the first preferred embodiment, each curved vertical wall terminates at a sufficient distance from the opposing curved outer wall and each curved outer wall is suitably oriented, so that some water discharged from a steering nozzle steered to one side is directed by the curved outer wall on that side through the aperture and out the discharge opening on the opposite side of the lateral steering passage. Water which flows around the port curved vertical wall of the deflector body is directed to the starboard discharge opening of the lateral steering passage; while water which flows around the port curved vertical wall of the deflector body is directed to the starboard discharge opening of the lateral steering passage.
The deflector body in accordance with the second preferred embodiment has a shape similar to that of the first embodiment described above, i.e., three vertical walls connected at a vertical juncture to form back-to-back J shapes having a common spine. The deflector body of the second preferred embodiment differs from the deflector body of the first preferred embodiment in two respects: (1) the former is pivotable about a vertical axis, whereas the latter is fixed; and (2) the lateral span from the end of the port curved vertical wall to the end of the starboard curved vertical wall of the former is greater than the corresponding span of the latter. These differences are related in that the ability of the deflector body to pivot in either direction makes it possible to extend the length of the curved vertical walls without decreasing the gap between the end of the curved vertical wall and the curved outer wall on the opposite side. The longer laterally curved vertical walls of the deflector body increase the angle by which the incoming water is turned, direct more water into the flow-reversing passages. This increases reversing thrust significantly without diminishing the steering thrust.
For embodiments wherein the deflector body pivots about a vertical axis passing through the central vertical wall, the central vertical wall will be referred to as a leading rudder. When the steering nozzle is centered, the steering nozzle discharge is split by the leading rudder. The respective streams are then diverted into the respective flow-reversing passages by the respective flow-deflecting walls of the deflector body. Steering, i.e., turning the steering nozzle about its pivot axis, in one direction applies unequal forces on the two sides of the deflector body, causing it to pivot in the opposite direction. This allows some of the nozzle discharge on the other side of the leading rudder to miss the deflector body, escape around the backside, and then flow through the aperture behind the deflector body, into the lateral steering passage, and out the steering passage discharge opening on the same side toward which the deflector body has been turned. This design produces high steering thrust during flow reversal.